The present invention relates to magnetic random access memory devices, and more specifically, to a high anneal temperature synthetic antiferromagnetic (SAF) freelayer and non-pinned reference layer for magnetic random access memory (MRAM) devices.
MRAM devices require the use of a storage and a reference layer. The storage layer is often comprised of a ferromagnetic layer which is fixed in magnetic orientation in spite of the influence of magnetic fields or spin torques by the pinning effects of an antiferromagnetic layer adjacent to it. In addition, SAF storage layers are implemented in MRAM with certain advantages. For example, it appears that higher activation energy can be obtained for equivalent switching currents when using a SAF structure versus a simple single free layer. Currently, the results in this example are obtained with low-temperature annealing and processing. However, for many semiconductor applications (particularly for embedded memory applications) it is important that the process be compatible with existing CMOS fabrication requirements. In practice, this means that the MRAM device must be able to withstand high temperature annealing and processing, with temperatures in the range of 400° C. for 1 hour total exposure time. Currently, it is also possible to fabricate SAF structures, which survive 400° C. anneals, demonstrating strong coupling in the SAF. Spin torque switching has been observed for anneal temperatures of up to 350° C. However, the current density can be too large to be practically employed and even for these demonstrations, the activation energy reported was only 62 kT. For applications in MRAM, an activation energy of at least 80 kT is typically required. In addition, conventional devices lose pinning and also magnetoresistance even for anneal temperatures below 400° C.